Siphoning metal



1934- v. c. DOERSCHUK ET AL 1,944,733

INVENTORS V/c Toe 62 flOEEJC'HI/K ATeW/A Q SCHOEFFEL SIPHONING METALFiled Oct. 22, 1932 TTORNEY.

Patented Jan. 23, 1934 SIPHONING METAL Victor C. Doerschuk and Erwin G.Schoeffel,

Massena, N. Y., assignors to Aluminum Company of America, Pittsburgh,Pa., a corporation of Pennsylvania 7 Application October 22, 1932.Serial No. 639,106

19 Claims. (01. 26638) num, which oxidizes quite rapidly at temperaturesabove its melting point. In the production and preparation of suchmetals a series of transfers is usually involved, and the turbulenceresulting from the discharge of an open stream of metal leads to theinclusion of considerable quantities of dross or oxidation producttherein at each transfer. Furthermore, mechanical difficulties of anequally troublesome nature are frequently encountered in the opentransfer of molten metals, and especially in the removal of moltenaluminum from reduction pots, which in the past have generally beendischarged by tapping a side of the pot. The tapping operation requiresa large amount of labor, leads to frequent accidents, and sometimes doesnot produce the results de-.- sired because the tapping pin goes astrayand pierces the wall of the container above the hearth.

The principal object of this invention is to overcome the difficultiespreviously encountered in the transfer of molten metals and especiallyin the transfer of molten aluminum. A further object of the invention isto provide an apparatus for transferring molten metal quietly andwithout contamination or oxidation. A specific object of the inventionis to provide an improved method of removing aluminum from electrolyticreduction pots. i

A further object of the invention is to provide a siphon coatedinternally with a protective layer of congealed refractory material andadapted for use in the quiet transfer of metal. A further object is toprovide a siphon which will withstand continued use at elevatedtemperatures and which is so designed that the cleaning and replacementof parts may be readily effected when desired. Further objects willappear upon reference to the following description and the accompanyingdrawing, in which:

. Fig. 1 is a diagrammatic view partly in elevation and partly invertical section of one form of siphoning apparatus adapted tothe'objects of the present invention; and

Fig. 2 is an elevatlonal view with parts broken away of a modified formof part of the apparatus shown in Fig. 1.

Referring to the drawing, in which like reference numerals are used todesignate like parts, a siphon, generally designated by the numeral 1,is shown which comprises a body, preferably tubular in form, with itscenter portion 2 substantially U-shaped. This siphon is preferably madeof heat-resisting cast iron. The discharge end 3 and the intake end 4 ofthe siphon are, in the preferred embodiment of our invention, providedwith thickened walls to increase their heat capacity and prolong theirlife, and to produce other results which will hereinafter appear. Theslphon ends 3, and 4 may be formed integrally with the center portion 2as shown in Fig. 1. Frequently, however, it is preferable to havethe'siphon ends detachable from the center portion in order that they may bereadily cleaned or replaced, and in such case a siphon of the form shownin Fig. 2, having suitable flange joints 5 or connections of othersuitable form provided between the center portion of the siphon body andone or both of the end sections thereof, may be used. v

Iniermediate the ends of the siphon body and preferably forming a partof the center portion 2 thereof, at or near its highest point, a base ormounting 8 is provided on which a, member enclosing a surge chamber 9 issecured by the joint 10. The cross sectional area of the surge chamberis preferably considerably larger than the cross sectional area of thetubular passage through the siphon body, with which it is preferably inconstant communication. The upper end of the surge chamber is providedwith a pipe 12 or other suitable outlet connected by means of a flexibletube or the like with an exhauster, suction pump, or other suitablemeans 13 adapted to withdraw air or other gas from the surge cham- 95her and siphon body and produce a partial vacuum therein. A ring or hook9b may be secured to the surge chamber in any suitable manner,'ifdesired, for attachment to a crane or other means for raising orlowering the siphon, and a handle 90 100 may be connected to the surgechamber or some other part of the siphon to assist in bringing it to thedesired position.

Whilethe invention herein described is broadly applicable to the'transfer of molten metals m5 generally, especially advantageous anddesirable results are obtained when the invention is applied to thetransfer of easily oxidizable metals and particularly aluminum, and moreparticularly when applied to the transfer of molten alun minum fromelectrolytic reduction pots. The invention will therefore be described,by way of example, with reference to the last-named application.

We have found that in using a siphon of the type herein described, it ishighly advantageous,

and in many cases necessary, to the quiet transfer of metal withoutcontamination thereof to provide the metal-contacting portions of thesiphon assembly with a layer 15 of congealed refractory material of suchcomposition that it will not in itself cause contamination of the moltenmetal. This refractory material should also have a melting point higherthan the temperature of the metal to be transferred. A salt of the metalbeing transferred, or a mixture of salts, is generally suitable for thispurpose. In the case of the transfer of aluminum, the molten bath whichis used in the electrolytic reduction pots in which aluminum is producedis the preferred protective material, as it has no injurious effect onthe metal, is readily separated therefrom, and is often available atplaces where molten aluminum is to be transferred. This bath usuallyconsists of natural or artificial cryolite, which is essentially amixture of fluorides of sodium and aluminum, with or without theaddition of smaller quantities of other ingredients, such as aluminumoxide, dissolved therein.

The application of a congealed coating 15 of refractory material to themetal-handling surfaces of the siphon assembly may be accomplished inseveral ways, the most practical of which is to draw molten refractorymaterial through the siphon passage and there congeal it to form asmooth and even coating. For instance, when molten aluminum is to betransferred from a reduction pot to a crucible or other receiver, thecoating may be applied in a manner which is best understood by furtherreference to the drawing, in which a conventional cell 14 for theelectrolytic reduction of aluminum is shown, with a crucible 16positioned adjacent thereto for receiving the molten metal. In theoperation of the cell or reduction pot 14 in known manner, aluminadissolved in the molten bath 17 is electrolytically reduced to formmolten aluminum, which sinks to the bottom of the pot and forms a layer18 adjacent the bottom lining 19, while a crust 20 is usually formed onthe surface of the bath. The siphon 1 is preferably preheated at leastsumciently to remove surface moisture, and its metalreceiving end orintake end 4 is inserted through the crust 20 and into the molten bathof cryolite 17. The discharge end 3 of the siphon is then closed toexclude air, as by means of a fusible plug or cover or, as is generallymore convenient,

by surrounding the discharge end of the siphon with a seal of the moltenbath, which may be held in the ladle 22. By means of the mechanism 13suction is applied to the siphon, creating a partial vacuum therein andcausing the molten bath to rise through the siphon and completely fillthe passage thereof as well as the lower part of the surge chamber 9. Ifduring this process the walls of the siphon are at a temperaturesomewhat below the melting point of the bath, the bath in contact withthe walls of the siphon and the surge chamber will congeal and form aprotective coating thereon.

The siphon is now ready for use, with or with- Suction is preferablyapplied continuously by the exhauster 13, at least until the flow ofmolten aluminum through the siphon is established, and usuallythroughout its transfer, but the suction may be released to allow thebath to drain from the siphon before starting the flow of aluminum ifdesired. The ladle 22, when used, is usually kept in the position shownin Fig. 1 until the layer of molten aluminum in the receiving vessel 16is deep enough to cover the discharge end 3 of the siphon, and it isthen withdrawn. If the suction is released to allow the siphon to drainbefore starting the flow of aluminum, however, the ladle 22 may beemptied of bath, filled with molten aluminum, and returned to theposition shown, where it is preferably held until the level of the metalin the crucible 16 is above the discharge end 3 of the siphon. The ladlehas a two-fold function, whether it is initially filled with bath orwith molten metal, as it seals the end of the siphon and excludes airtherefrom when the suction is first applied, and then diffuses the metaldischarged from the siphon, reducing the turbulence of its flow into thereceiver and preventing spattering. When molten metal is present in thereceiver 16 in such quantity that it covers the end 3 of the siphon, so

that discharge from the siphon takes place beneath its surface, thepresence of the ladle is unnecessary.

During the transfer of the molten aluminum, the intake end 4 of thesiphon is positioned substantially at the bottom of the cell 14, and itsedge may be provided with short legs or analogous projections tofacilitate entrance of the molten metal into the siphon passage, butirregularities in the surface of the lining l9 usually make thisunnecessary. The partial vacuum created in the siphon must initially besufficient to overcome the static head of the molten material in theintake portion of the siphon, and it is pref erable to maintainthroughout the transfer of metal a vacuum sumcient to hold moltenmaterial in the entrance to the surge chamber. When so operated, asiphon equipped with a surge chamber of suitable size and having itsmetal-contacting surfaces coated with congealed refractory materialwhich is unreactive with the metal transferred, as describedhereinabove, will efiect a quiet transfer of metal from one container toanother with a minimum of contamination and with a rapidity and economywhich are highly desirable in commercial operation.

When several transfers of metal are to be made in quick succession withthe same siphon, which is frequently the case, it is not necessary tocoat the siphon as a separate step before each transfer. Enough bath iscongealed on the siphon while lowering it into position, or during thetransfer of the metal, or after the transfer when a small amount of bathis usually drawn over to be sure that the metal is completely recovered,to keep the protective layer intact after a thorough initial coating hasbeen applied. Small amounts of bath delivered by the siphon into thecrucible or other receiver 16 are not troublesome, as this materialrises to the surface of the metal and is readily skimmed off orotherwise removed in known manner.

Considerable advantage is gained by designing the siphon with removabletips, such as the sections 3 and 4 shown in Fig. 2, because, after longuse, the tips may require replacement, or the layer of congealed bath orother refractory material may build up, or other stoppages may oocur, sothat the siphon has to be cleaned. This is readily accomplished afterremoval of the surge chamber and the detachable ends, which gives easyaccess to all parts of the siphon for cleaning, replacement or repairs.The surge chamber mounting provides a large and conveniently locatedopening through which any temporary stoppage of the siphon tube may berelieved.

During the operation of the siphon or siphon pump, it is necessary tooperate the vacuum pump 13 continuously to obtain the best results. Wehave found in practice that maintenance of a vacuum of about 3 inches ofmercury throughout the transfer of the aluminum is generallysatisfactory, although apparently not critical. With the surge chamberopening from the siphon passage at substantially its highest point andmaintained at a suitable vacuum, gas is continuously withdrawn from themolten metal during its transfer and escapes without interruption of themetal flow. The metal is thus at least partially de-gassed during itstransfer, and its quality is improved as compared with metal transferredby the gravity method of tapping. One function of the surge chamber isto prevent plugging of the pipe 12, the vacuum hose connected thereto,and the pump 13. The coating of congealed bath or other refractorymaterial on the metal-contacting surfaces of the siphon protects themolten metal from contamination and also protects the siphon from attackby the metal and from deterioration due to the high temperature of themetal.

While our invention has been described with special reference to apreferred embodiment and application thereof, it will be obvious tothose skilled in the art that certain changes or modifications can bemade therein, in addition to those described by way of examplehereinabove, without departing from the spirit of our invention. Weclaim as our invention: l. The process of siphoning molten metal, whichcomprises drawing through a siphon molten material having a highermelting point than the metal, cooling said material by contact with thesiphon to form a protective coating on the inner surface thereof, anddrawing the molten metal through the siphon.

2. The process of siphoning molten metal, which comprises drawingthrough a siphon a mixture of molten salts having a higher melt ingpoint than the metal and substantially unreactive therewith, coolingsaid mixture by contact with the siphon to form a protective coating onthe inner surface thereof, and drawing the molten metal through thesiphon.

3. The process of providing siphons for the transfer of molten metalwith linings of refractory material, which comprises drawing through asiphon molten material having a higher melting point than the metal tobe trans ferred and refractory thereto, and cooling said material bycontact with the siphon to form a protective coating on the innersurface thereof.

t. The process of transferring molten metal from a vessel wherein it iscontained to a receiver, which comprises sealing one end of a siphon toexclude air, inserting the other end of the siphon in molten materialhaving a higher melting point than the metal to be transferred andapplying a suction to the siphon to draw said molten materialtherethrough, the siphon being at a temperature such that at least aportion of the molten material therein is congealed to form a protectivecoating on the interior of the siphon, andthen inserting the intake endof the siphon into the molten metal and applying suction to draw themolten metal through the siphon into the receiver.

5. The process of transferring molten metal from a vessel wherein it iscontained to areceiver, which comprises inserting the discharge end of asiphon into said receiver and temporarily closing said discharge end,lowering the intake end of the siphon into a body of molten materialhaving a higher melting point than the metal to be transferred andapplying a suction to the siphon to draw said molten materialtherethrough, the siphon being at a temperature such that at least aportion of the molten material is congealed thereby to form a protectivecoating thereon, and then lowering the intake end of the siphon into themolten metal while applying suction to induce a flow of said metalthrough the protectively-coated siphon into said receiver.

6. The process of transferring molten aluminum which comprises drawingthrough a siphon a fused salt bath having a higher melting point thanaluminum and substantially unreactive therewith, cooling at least aportion of said bath by contact with the siphon to form a protectivecoating on the inner surface thereof, and drawing the molten aluminumthrough the protectively-coated siphon.

7. The process of transferring molten aluminum, which comprises drawingthrough a siphon a fused salt bath consisting essentially of a mix tureof sodium and aluminum fluorides having a higher melting point thanaluminum, cooling at least a portion of said bath by contact with thesiphon to form a protective coating on the inner surface thereof, anddrawing the molten aluminum through the protectivelycoated siphon.

8. The process of transferring molten aluminum into a receptacletherefor from an electrolytic reduction pot containing a layer of saidmolten aluminum and a superposed layer of molten electrolytic bath,which comprises inserting the discharge end of a siphon into saidreceptacle and sealing said discharge end with molten material from areduction pot to exclude air, and lowering the intake end of the siphonthrough the layer of molten electrolytic loath into the molten metal insaid reduction pot while applying suction to the siphon, thereby drawingmolten bath through the siphon where it is congealed by the siphon toform a protective coating thereon and then drawing molten aluminumthrough the protectively-coated siphon into the receptacle.

9. In a process of transferring molten metal into a receptacle therefor,the combination of steps comprising coating the inner surface of asiphon with a congealed layer of material having a higher melting pointthan the metal and drawing the molten metal through the coated siphonwhile continuously applying suction thereto.

10. In a. process of transferring molten aluminum into a receptacletherefor, the combination of steps comprising coating the inner surfaceof a siphon with a congealed layer of salts having a higher meltingpoint than aluminum and substantially unreactive therewith, and drawingmolten aluminum through the coated siphon into said receptacle whilecontinuously applying suction to the siphon.

11. In a process of transferring molten aluminum into a receptacletherefor, the combination of steps comprising coating the inner surfaceof a siphon with a congealed layer of salts consisting essentially ofsodium and aluminum fluorides and drawing molten aluminum through thecoated siphon into said receptacle while continuously applying suctionto the siphon.

12. In a process of transferring molten aluminum from an electrolyticreduction pot which comprises drawing the aluminum through a siphon at.least partially coated with a congealed layer of the electrolytic bath,the step comprising closing the discharge end of the siphon with moltenmaterial withdrawn from the reduction pot while applying suction toinduce a flow of molten material through the siphon.

13. A siphon for transferring molten metal comprising a substantiallyU-shaped tube coated on its inner surface with a congealed layer ofmaterial having a higher melting point than the metal to be transferredand operatively connected intermediate its ends with means adapted toapply a suction to the tube.

14. A siphon for transferring molten metal comprising a substantiallyU-shaped tube coated on its inner surface with a congealed layer ofmaterial having a higher melting point than the metal to be transferredand provided intermediate its ends with a surge chamber of materiallygreater cross-sectional area than the tube, said chamber being connectedwith means adapted to create a partial vacuum in the tube.

15. A siphon for transferring molten metal, comprising a hollowsubstantially U-shaped member with a tubular passage therethrough, thewalls of said passage being thickened near the ends of said member, andsaid member being provided intermediate its ends with a surge chamber ofgreater cross-sectional areathan the said tubular passage and connectedtherewith, said chamber being also connected with means adapted to applya suction to the passage to draw molten metal therethrough.

16. A siphon for transferring molten metal, comprising a curved memberwith a passage therethrough, said member consisting of at least onedetachable end portion having increased wall thickness throughout atleast a part of its length, and a center portion detachably connected tosaid end portion, said center portion being also detachably connectedwith a member enclosing a surge chamber of greater cross-sectional areathan the said passage and communicating therewith, and said surgechamber being operatively connected with means for producing a partialvacuum therein.

17. In a siphon for transferring molten metal, a surge chambercommunicating with a passage through the siphon, said chamber being ofmaterially greater cross-sectional area than the passage, and beingreadily detachable therefrom.

18. A siphon for transferring molten aluminum from electrolyticreduction pots to receptacles therefor, comprising a substantially U-shaped tube coated on its inner surface with a congealed layer composedprincipally of a mixture of sodium and aluminum fluorides having ahigher melting point than the aluminum, and opera- 09 tlvely connectedintermediate its ends with means adapted to create a partial vacuum inthe tube.

19. A siphon for transferring molten aluminum from electrolyticreduction pots to recepta- 5 cles therefor, comprising a substantiallyU-shaped tube coated on its inner surface with a congealed layercomposed principally of a mixture of sodium and aluminum fluorideshaving a higher melting point than the aluminum and providedintermediate its ends with a surge chamber of materially greatercross-sectional area than the tube, said chamber being connected withmeans adapted to create a partial vacuum therein to draw molten aluminumthrough the siphon.

VICTOR C. DOERSCHUK. ERWIN G. SCHOEFFEL.

